An investigation was made of the fast diffusion of Si from deposited surface layers when oxidized in an Ar/H2O ambient. This revealed the presence of excess As which was formed by the oxidation of Ga which originated from the substrate, and was used to explain the enhanced diffusion of Si into the substrate. The formation of SiO2 on the surface during oxidation prevented the loss of the excess As, which then accumulated in the remaining Si film. The use of higher H2O partial pressures during oxidation produced higher As/Si ratios; thus resulting in an increase in Si diffusion depth and concentration. However, the n-type carrier concentration decreased with increasing As/Si ratios in the remaining Si layer. A second non-oxidizing annealing treatment, of samples from which the SiO2 and Si layer had been removed, had differing effects upon the carrier concentration; depending upon whether the As was free to escape from the substrate. The results indicated that excess As-related defects, such as Ga vacancies, were probably responsible for n-type compensation in fast diffused samples.

R.C.Keller, C.R.Helms: Applied Physics Letters, 1995, 67[3], 398-400